1. Field of the Invention
The present invention relates to a silver halide photographic material and, more particularly, to a silver halide photographic material having improved antistatic properties.
Supports used in photographic materials are electric insulators and are easily electrified when they are rubbed against or peeled away from other objects. The resulting static charges on the supports can cause various troubles such as attraction of dust particles, the occurrence of electric shocks, and of fire. In the manufacture of silver halide photographic materials using such supports, frequent cycles of friction and peeling occur in various steps such as winding, rewinding, application of light-sensitive layers and various other coating layers, and transport of the web being dried. If the static electricity that has been generated as a result of such friction and peeling phenomena is discharged, the photosensitive material carrying light-sensitive layers becomes exposed and will produce static marks after development (i.e., uneven development due to static buildup). Such static marks and various other troubles due to the deposition of foreign matter such as dust particles will also occur during the use or processing of the manufactured photographic materials. Since the severity of static marks is increased as the sensitivity of the photographic materials increases, there is a growing need to establish a technique for minimizing the occurrence of static marks on modern photographic materials that feature ever increasing degrees of sensitivity. In addition, the current manufacturing practice of photographic materials involves an increased chance of their being handled under hostile conditions as a consequence of faster coating and drying operations and processing with a high-speed automatic developer, and this has given another impetus to the development of a technique that is capable of minimizing the occurrence of various troubles due to static buildup.
Various methods have been known to be effective against the troubles associated with static electricity on photographic materials. According to the most popular and commonly used method, the back side of a photographic material (viz., the side on which no light-sensitive layer is formed and is hereinafter referred to as the BC layer) is provided with a layer containing an ion-conductive material, such as a gelatin layer containing sodium polyphosphoric acid, a diacetylcellulose layer containing an electrolyte-containing metal oxide sol, or an ionic polymer layer, that imparts electrical conductivity to the photographic material and thereby decreases the chance of static buildup. However, if this method is applied to the actual silver halide photographic material, certain undesirable phenomena occur in various ways: for instance, if a roll of photographic material or stacked sheets of photographic material are placed in a humid atmosphere, adjacent layers will stick to each other; if this "blocking" problem does not occur, a phenomenon that may be described as "time-dependent deterioration of the electrical conductivity of a film roll in high humidity" will occur and the electrical conductivity of the BC layer in one specimen is reduced as a result of partial transfer of the ion-conductive material to the obverse surface (i.e., the side carrying silver halide emulsion layers) of another specimen with which the first specimen comes in contact.
With a view to solving these problems, it has been proposed that a protective layer of a hydrophobic polymer be provided on the electroconductive layer. This method is effective in preventing the occurrence of blocking in high humidity but does not make any substantial contribution to reduction in the time dependent deterioration of electroconductivity of a film roll in high humidity. If the overlying hydrophobic layer is of adequate thickness, the diffusion of ions from the conductive layer can be satisfactorily prevented but then the support will experience too much curling to be suitable for use in practical applications.
Attempts have therefore been made to suppress the time-dependent deterioration of the conductivity of the electrically conductive layer by rendering it hydrophobic before it is coated with a hydrophilic layer. For instance, British Patent No. 1,172,999 discloses a method of increasing the hydrophobicity of a conductive layer derived from an ethylenically unsaturated compound by forming it from a copolymer of a hydrophilic monomeric electrolyte and a hydrophobic monomer. Japanese Patent Application (OPI) No. 18728/1979 (the term "OPI" as used herein means an unexamined published Japanese patent application) shows the use of a comparatively hydrophobic ionene polymer having a dissociative group in the backbone chain. Japanese Patent Application (OPI) No. 59926/1979 proposes a method for producing a homogeneous film of an electrolyte-containing sol and a hydrophobic polymer, with the latter being dissolved in an organic solvent.
These methods which rely on the formation of a hydrophobic layer on an ion-conductive film that has been rendered hydrophobic are effective for the purpose of preventing the occurrence of blocking in a humid condition but are far less effective in minimizing the time-dependent deterioration of the electrical conductivity of a film roll in high humidity. Furthermore, the hydrophobic ion-conductive layer is low in electrical conductivity, eventhough increasing it has been the principal object of these approaches, and in practice they fail to provide photographic materials with the desired antistatic properties.
Numerous efforts have also been made to improve the antistatic properties of silver halide emulsion layers by, for example, incorporating various hygroscopic substances, water-soluble inorganic salts, certain surfactants and polymers in either the silver halide emulsion layers or overlying protective layers. Surfactants are particularly important antistatic agents and among the so far proposed surfactants are anionic, betaine-based and cationic surfactants of the types described in U.S. Pat. Nos. 3,082,123, 3,201,251, 3,519,561 and 3,625,695; West German Patent Nos. 1,552,408 and 1,597,472; Japanese Patent Application (OPI) Nos. 85826/1974, 129623/1978, 159223/1979, 19213/1973; Japanese Patent Publication Nos. 39312/1971, 11567/1974, 46755/1976 and 14417/1980; and nonionic surfactants of the types described in Japanese Patent Application (OPI) No. 80023/1977, West German Patent Nos. 1,422,809 and 1,422,818, and Australian Patent No. 54,441/1959.
However, the performance of some of these substances depends not only on the type of specific film support but also on the specific photographic composition. One substance exhibits good results when it is used with a certain film support or photographic emulsion and other photographic constituent elements but is entirely ineffective for antistatic purposes if used with other film supports or photographic constituent elements. Alternatively, some materials that display superior antistatic properties cause adverse effects on the photographic characteristics of a photographic emulsion, such as sensitivity, fog, granularity and sharpness. For these reasons, extreme difficulty has been encountered in trying to incorporate these substances into photographic materials.
Nonionic surfactants having a polyoxyethylene unit display comparatively good antistatic properties and ethylene oxide addition polymers of the condensation product of phenol and formaldehyde (as described in Japanese Patent Publication Nos. 8742/1972, 9610/1976, 18178/1982, 19406/1982, 43729/1983, Japanese Patent Application (OPI) Nos. 48520/1979, 101140/1981, 80648/1985, 208743/1983, 203435/1983, etc.) have proved to be fairly effective antistats as they cause minimal adverse effects on the photographic characteristics of a photographic material and yet their performance is not highly dependent on the type of specific film support or photographic composition.
If a silver halide emulsion or protective layer employing a nonionic surfactant having a polyoxyethylene unit is provided on a support that has the aforementioned ion-conductive film formed on the BC layer, a remarkable improvement is attained in the ordinary antistatic performance but, on the other hand, the defect inherent in the technique of forming an ion-conductive film on the BC layer, namely, the time-dependent deterioration of the electrical conductivity of a film roll in high humidity, becomes even more pronounced, and if the photographic material prepared by employing this technique is handled under dry conditions after storage in a humid atmosphere, static marks and other troubles due to static buildup will frequently occur.
Besides these nonionic surfactants, fluorine-containing compounds that inhibit static buildup by generating weak electricity are also known as superior antistats. Such fluorine-containing compounds include F-containing surfactants and F-containing polymers: compounds of the first class are shown in such patents as British Patent Nos. 1,293,189, 1,259,398, U.S. Pat. Nos. 3,666,478, 3,754,924, 3,775,236, Japanese Patent Application (OPI) Nos. 48520/1979, 114944/1981, 161236/1975, 151127/1976, 59025/1975, 113221/1975, 99525/1975, Japanese Patent Publication Nos. 44411/1981, 6577/1982, Japanese Patent Application Nos. 83566/1982, 80773/1982, Japanese Patent Application (OPI) Nos. 84712/1978, 64228/1982, 258542/1985, and general references such as I & EC Product Research and Development, 1 (3), September 1962 and Abura Kagaku (Oil Chemistry), 12, (12), pp. 652-653, 1963; while compounds of the second class are described in such patents as Japanese Patent Application (OPI) Nos. 158222/1979, 129520/1977, 23828/1974, British Patent Nos. 1,352,975, 1,497,256, U.S. Pat. Nos. 4,087,394, 4,016,125, 3,240,604, 3,679,411, 3,340,216, 3,632,534, Japanese Patent Application (OPI) Nos. 30940/1973, 129520/1977, 44973/1985, 210613/1985, 11342/1982, 76742/1985, 80849/1985, and U.S. Pat. No. 3,753,716. It has been known to improve the antistatic properties of light-sensitive materials by incorporation of these fluorine-containing compounds.
If a silver halide emulsion or protective layer that contains one or more of these fluorine-containing compounds is provided on a support that has the aforementioned ion-conductive film formed on the BC layer, the accelerated deterioration of the electrical conductivity of the BC layer in a film roll at high humidity, which is the problem resulting from the use of a non-ionic surfactant having a polyoxyethylene unit, can be reduced by a satisfactory degree. However, the antistatic effect of the fluorine-containing compounds in the emulsion layer or protective layer is decreased if the film roll is stored in a humid atmosphere, and the chance of static marks and other troubles associated with static buildup occurring is eventually increased.
As described above, if photographic materials are stored in a stacked form under humid conditions, with the ion-conductive layer on the back side of a support being in contact with the emulsion or protective layer of an adjacent sheet of photographic material that contains a fluorine-containing compound or a nonionic surfactant having a polyoxyethylene unit, the antistatic effect of the ion-conductive layer is deteriorated to increase the chance of the development of static marks and other troubles associated with static buildup.
Modern silver halide photographic materials are designed to meet the ever growing demand for higher sensitivity and amenability to rapid processing with developers of a very small size. These factors contribute to a greater chance of static marks being produced as a result of increased triboelectrification. In developing machines of a small size, the emulsion coated side of a silver halide photographic material is kept in contact with transport rollers under strong force and, hence, has a great tendency to develop static marks across its entire surface. In order to avoid these problems, there has been a strong need to design a silver halide photographic material having improved antistatic properties.